WASHINGTON -- Dust storms swirling out of Africa's Sahara Desert may help reduce hurricane activity in the Atlantic Ocean, a new study suggests. The findings aren't conclusive, but researchers led by Amato T. Evan of the University of Wisconsin-Madison found that years with more African dust had fewer tropical storms and years with less dust had more storms.

The study is reported in Tuesday's issue of Geophysical Research Letters.

Evan and his colleagues used satellite images to study the amount of African dust blown out over the Atlantic for the years 1982-2005 and compared that with tropical storm activity.

"While we cannot conclusively demonstrate a direct causal relationship, there appears to be a robust link between tropical cyclone activity and dust transport," they concluded.

"People didn't understand the potential impact of dust until satellites allowed us to see how incredibly expansive these dust storms can be," Evan said in a statement. "Sometimes during the summer, sunsets in Puerto Rico are beautiful, because of all the dust in the sky _ well that dust comes all the way from Africa."

Co-author Jonathan Foley, also of the University of Wisconsin, added: "These findings are important because they show that long-term changes in hurricanes may be related to many different factors."

Several recent studies have indicated a potential relationship between warming sea surface temperatures and increases in either the strength or number of tropical storms.

Other researchers have suggested a link between rain in North Africa and an increase in tropical storms, resulting from more easterly wave disturbances entering the Atlantic from Africa.

Dust blowing off the Sahara can spread widely and it is not unusual for it to be detected in the Caribbean and Florida.

The researchers suggest three possible ways the dust can affect storms:

_ By introducing dry air into a storm it causes downdrafts, blocking the rising streams of air needed to fuel a storm.

_ Midlevel winds accompanying the Saharan air cause wind shear, a change in direction with altitude that prevents rising currents from growing into storms.

_ Warmth absorbed by the dust in the air can stabilize conditions, again blocking rising air.